Thermochromic indicator materials with controlled reversibility

ABSTRACT

A thermal indicator material which comprises a plurality of polythiophenes having a second low temperature color and a high temperature color. The polythiophenes are structured and arranged to exhibit a color change from the second low temperature color to the high temperature color when the thermal indicator material is exposed to a temperature that meets or exceeds a predetermined temperature and to exhibit a color change from the high temperature color to a first low temperature color when the thermal indicator material is exposed to a decline in temperature from a temperature that meets or exceeds the predetermined temperature to a temperature of within the range of between about 5 to 20° C. below the pre-determined temperature that occurs in a time period of greater than 2.0 seconds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/405,027, filed Mar. 16, 2009, which is acontinuation of U.S. patent application Ser. No. 11/024,326, filed Dec.28, 2004, and issued as U.S. Pat. No. 7,517,475, issued Apr. 14, 2009.U.S. patent application Ser. No. 11/024,326, filed Dec. 28, 2004, claimsthe benefit of U.S. Provisional Application Ser. No. 60/392,452 filedJun. 28, 2002, and International Patent Application Serial No.PCT/US2003/020537 filed Jun. 30, 2003, all applications of which arehereby incorporated by reference in their entireties. U.S. patentapplication Ser. No. 11/024,326 filed Dec. 28, 2004 is related toInternational Patent Application Serial No. PCT/US02/22079, filed Jan.10, 2002 and U.S. patent application Ser. No. 09/758,075, filed Jan. 10,2001 now U.S. Pat. No. 6,706,218, both applications of which are herebyincorporated by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and, theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of FY01-PS10awarded by USDOT.

FIELD OF THE INVENTION

The invention relates to thermo chromic indicator materials comprised ofpolythiophenes.

DESCRIPTION OF RELEVANT ART

Polythiophenes are known for their electrically conductive properties.One technique used to study polythiophenes is to analyze associatedcolor changes when the temperature of the polythiophene is varied. Colorchanges provide insight into the electro-conductive properties of thepolymer. There are numerous patent and literature citations whichdescribe this work.

In many instances it is clearly desirable to know when an object orarticle reaches or has exceeded a specific temperature simply by viewingthe object and noting that at least a portion of the object hasexhibited a color change. Viewing includes visual observation by anindividual or detection of color change by a sensor, which sensor wouldoutput a signal to be detected in any suitable manner.

For example, the useful life of many products can become comprised ifexposed to temperatures above a pre-determined temperature. Accordingly,a need exists for a thermal indicator that exhibits a controlled colorchange indicative of when such products, e.g., food and protective firesuits, have been exposed to the pre-determined temperature. The presentinvention addresses this need.

BRIEF SUMMARY OF THE INVENTION

Broadly, the invention comprises a thermal indicator material comprisedof temperature sensitive polymers that exhibit a visually detectablecolor change at a proscribed temperature within the range of betweenabout −30 to 150° C. The visual detection can include visual observationby an individual or detection of the exhibited color change by a sensor,which sensor would output a signal to be detected in any suitablemanner. The temperature of the color change (hereinafter referred to asthe thermo chromic transition) can be adjusted by syntheticallymodifying the thermo chromic polymers. Upon heating a sample of thethermal indicator material to a high temperature within the range ofbetween about 130° C. and 160° C., preferably 140° C., followed by rapidcooling, the sample will maintain a new color at low temperatures withinthe range of between about 0° C. and 30° C., preferably 20° C. When thesample is reheated above the thermo chromic transition and allowed tocool slowly, the sample reverts to the original low temperature color.This controlled reversible thermochromic transition results from theheating of the sample to a high temperature followed by the rapidcooling of the sample. The temperature sensitive polymers, when used aspigments to mark an item, can indicate whether the marked item has metor exceeded a pre-determined temperature at any time after marking.Items coated with the polymers show no detectable loss of the mark aftermore than one year of storage below the thermo chromic transitiontemperature. The thermo chromic polymers can be dispersed in commercialplastics (polyurethane, polystyrene, polyethylene, etc.) at lowconcentrations and retain the controlled reversibility. The temperaturesensitive polymers can also be used as a pigment for inks.

The thermochromic polymers are generally of the structure:

wherein R₁-R₆=a hydrogen, substituted or unsubstituted alkyl radical,substituted or unsubstituted alkoxy radical, substituted orunsubstituted aryl radical, substituted or unsubstituted thioalkylradical, substituted or unsubstituted trialkylsilyl radical, substitutedor unsubstituted acyl radical, substituted or unsubstituted esterradical, substituted or unsubstituted amine radical, substituted orunsubstituted amide radical, substituted or unsubstituted heteroaryl orsubstituted or unsubstituted aryl radical

n is between 1 and 1000,

m is between a and 1000, and

1 is between 1 and 1000.

Compound I has reversible color changes upon temperature variation. Thetemperature of the color change and the reversibility is dependent uponthe structure of the polymer or the oligomer. The mechanism for thethermo chromic transition is based on a two-step process. At lowtemperature the polymer has the conjugated repeat units (responsible forcolor) in a planar conformation and the substituents of thepolythiophene chain are ordered into a lattice. As the temperature israised, the side chain lattice melts and the resulting disorder allowsthe main chain repeat units to twist away from planarity as shown belowin Scheme 1:

The twisting of the polythiophene units increases the band gap whichresults in a blue shift of the optical absorption as shown in Scheme 2:

Polythiophenes with long sidechains are believed to have sharpthermochromic transitions due to the two-phase morphology. The meltingof the sidechains causes a zipper effect, which results in a sharpthermo chromic transition. When polythiophenes with long side-chainsfilms are rapidly cooled the side chain lattice freezes before the mainchain twists back to a planar conformation. Since the main-chain islocked in a staggered conformation the color of the material has ashorter wavelength absorption than polythiophenes that are cooled slowlyallowing the main-chain thiophene units to become planar.

In one aspect, the invention comprises a method for producing a thermalindicator material which comprises a plurality of compounds having thefollowing structure:

wherein R₁-R₆ is a hydrogen, substituted or unsubstituted alkyl radical,substituted or unsubstituted alkoxy radical, substituted orunsubstituted aryl radical, substituted or unsubstituted thioalkylradical, substituted or unsubstituted trialkylsilyl radical, substitutedor unsubstituted acyl radical, substituted or unsubstituted esterradical, substituted or unsubstituted amine radical, substituted orunsubstituted amide radical, substituted or unsubstituted heteroaryl orsubstituted or unsubstituted aryl radical, n is between 1 and 1000, m isbetween 0 and 1000, and l is between 1 and 1000. The compounds have afirst low temperature color and are structured to exhibit a hightemperature color when the compound is exposed to temperatures above apre-determined temperature. The compounds are heated to a temperaturewithin the range of between about 130° C. and 160° C., preferably 140°C. to form heated compounds. The heated compounds are cooled within atime period of less than 2.0 seconds, preferably 0.1 seconds, to atemperature within the range of between about 0° C. and 30° C.,preferably 20° C., to form cooled compounds. The cooled compoundsexhibit a second low temperature color and exhibit a color change fromthe second low temperature color to the high temperature color when thethermal indicator material is exposed to a temperature that meets orexceeds the pre-determined temperature and exhibit a color change fromthe high temperature color to the first low temperature color when thethermal indicator material is exposed to a decline in temperature from atemperature that meets or exceeds the predetermined temperature to atemperature within the range of about 5 to 20° C. below thepre-determined temperature, the decline in temperature occurring in atime period of greater than 2.0 seconds, preferably 20 seconds. Thecompounds can be heated for a time period within the range of betweenabout 5 seconds to 1000 seconds, preferably 40 seconds. Thepredetermined temperature range of the compounds can be in the range ofbetween about −30 to 150° C., preferably 65 to 100° C.

In another aspect of the invention, the method further comprisesadmixing the cooled compounds with a carrier medium. The cooledcompounds can be present in the thermal indicator material in an amountof about 0.05 to about 25.0%, preferably 5.0% by weight based on thetotal weight of the thermal indicator material.

In yet another aspect of the invention, the pre-determined temperaturecan be 85° C., the first low temperature color is burgundy, the hightemperature color is yellow and the second low temperature color isorange.

In another aspect of the invention, R₁ and R₄ are C₂₀-C₅₀ alkyls orsubstituted alkyls, and R₂, R₃, R₅ and R₆ are H, n is 0.8, m is 0.2, and1 is, between 15 and 100.

In yet another aspect of the invention, the carrier medium comprises anink formulation.

In yet another aspect, the thermal indicator material produced by themethod will exhibit a color change from the high temperature color tothe second low temperature color when the thermal indicator material isexposed to a decline in temperature from a temperature that meets orexceeds the pre-determined temperature to a temperature within the rangeof between about 20 to 50° C. below the pre-determined temperature thatoccurs in a time period of less than 2 seconds.

The invention also comprises the thermal indicator materials produced bythe method as well as the thermal indicator materials admixed with acarrier material.

As used herein, the terms low temperature color means the color thepolythiophenes will exhibit below the pre-determined temperature andwhen the color change has either been completed or commenced. The termhigh temperature color means the color the polythiophenes will exhibitabove the pre-determined temperature and when the color change has beeneither completed or commenced.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 depicts polythiophene films of the invention on paper at: (a)room temperature; (b) above the thermo chromic temperature; (c)thermally marked with Sargent key; and (d) thermally marked with acircle;

FIG. 2 is a graph depicting the reflectance spectra of thermo chromicindicator materials of the invention below the thermo chromic transitionbefore marking, above the thermo chromic transition, and below thethermo chromic transition after marking;

FIG. 3 depicts polythiophene films of the invention on paper thermallymarked with a circle; and

FIG. 4 depicts polythiophene films of the invention on paper thermallymarked with a circle.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, a photograph depicting polythiophene films on paperat: (a) room temperature; (b) above the thermo chromic temperature; (c)thermally marked with Sargent key; and (d) thermally marked with acircle is shown. The films are comprised of a polythiophene wherein R₁and R₄ are —(CH₂)₂₁CH₃, R₂, R₃, R₅ and R₆ are H, n is 0.8, m is 0.2, andl is between 25 and 50. The films in FIG. 1 were spin coated from THFsolutions of the polythiophene onto paper. After spin coating, the filmswere heated with a heat gun to between 120 and 150° C. and then wereallowed to slowly cool (>2 seconds) to room temperature to remove anyresidual solvent. This provided the burgundy film shown in FIG. 1 a.Heating the film a second time to between 120 and 150° C. causes thefilm to change in color from burgundy to yellow as shown in FIG. 1 b.After heating films to between 120 and 150° C. the films can be rapidlycooled (0.1 seconds) by pressing a metal key onto the surface of thefilm. Rapid cooling to low temperature, 0 to 30° C., allows thegeneration of an orange mark in the form of a key. The remainder of thefilm, which cooled slowly, returns to the original low temperaturecolor, burgundy (FIG. 1 c). If the film is maintained at temperaturesbelow the thermo chromic transition of the polythiophene film (85° C.)the mark will be retained for more than a year. However, if the film isheated above 85° C. the mark will disappear. After heating films tobetween 120 and 150° C. the films can be rapidly cooled by pressingmetal fuse onto the film. Rapid cooling to low temperature, 0 to 30° C.,allows the generation of an orange mark in the form of a circle (FIG. 1d).

Referring to FIG. 2, a graph depicting the reflectance spectra of thermochromic indicator materials of the invention below the thermo chromictransition before marking, above the thermo chromic transition, andbelow the thermo chromic transition after marking. The films arecomprised of a polythiophene wherein R1 and R4 are —(CH2b CH3, R2, R3,Rs and R6 are H, n is 0.8, m is 0.2, and l is between 25 and 50.

Referring to FIG. 3, a photograph depicting polythiophene films on paperthermally marked with a circle. The films are comprised of apolythiophene wherein R₁ and R₄ are —(CH₂)₂₁CH₃, R₂, R₃, R₅ and R₆ areH, n is 0.8, m is 0.2, and l is between 25 and 50. The films in FIG. 3were spin coated from THF solutions of the polythiophene onto paper.After spin coating, the films were heated with a heat gun to between 120and 150° C. and then were allowed to slowly cool (>2 seconds) to roomtemperature to remove any residual solvent. The low 20 temperature filmsare red. After heating films to between 120 and 150° C. the films can berapidly cooled (0.1 second) by pressing a metal fuse onto the surface ofthe film. Rapid cooling to low temperature, 0 to 30° C., allows thegeneration of an orange mark in the form of a circle. The remainder ofthe film, which cooled slowly, returns to the original low temperaturecolor, red (FIG. 3). If the film is maintained at temperatures below thethermo chromic transition of the polythiophene film (75° C.) the markwill be retained for more than a year.

Referring to FIG. 4, a photograph depicting polythiophene films on paperthermally marked with a circle. The films are comprised of apolythiophene wherein R₁ and R₄ are —(CH₂)₂₁CH₃, R₂, R₃, R₅ and R₆ areH, n is >0.95, m is <0.05, and 1 is between 25 and 50. The films in FIG.4 were spin coated from THF solutions of the polythiophene onto paper.After spin coating, the films were heated with a heat gun to between 120and 150° C. and then were allowed to slowly cool (>2 seconds) to roomtemperature to remove any residual solvent. The low temperature filmsare purple. After heating films to between 120 and 150° C. the films canbe rapidly cooled (0.1 seconds) by pressing a metal fuse onto thesurface of the film. Rapid cooling to low temperature, 0 to 30° C.,allows the generation of a red mark in the form of a circle. Theremainder of the film, which cooled over more than 2 seconds, returns tothe original low temperature color, purple (FIG. 4). If the film ismaintained at temperatures below the thermo chromic transition of thepolythiophene film (95° C.) the mark will be retained for more than ayear.

The synthesis of compound(s) I is known in the art. In the synthesis ofcompound(s) I to exhibit the color change at the pre-determinedtemperature, e.g., for the series of poly(3-alkylthiophene)s, there isroughly an inverse correlation with the length of the n-alkanesubstituent and the temperature of the thermo chromic transition forboth the regiorandom (R₁=alkyl, R₄=alkyl, n˜0.8, m˜2, 1=40-80,R₂,R₃,R₅,R₆═H) and regioregular (R₁=alkyl, n=40-80, m=0, R₂,R₅,R₆═H),poly(3-n-alkylthiophene)s. For regiorandom polymers longer substituentssuch as n-hexadecyl have lower temperature thermo chromic transitions(81° C.) than shorter chain substituents such as n-octyl (130° C.). Theregioregular polymers have higher thermo chromic transitions than theregiorandom polymers but the same inverse correlation with chainlengthis observed. The n-hexadecyl and n-octyl have thermo chromic transitioncentered around 125 and 175° C. The thermo chromic transitiontemperatures are dependent upon the molecular weight of the polymer.Lower molecular weight polymers have lower thermo chromic transitiontemperatures while higher molecular weight polymers have higher thermochromic transition temperatures.

In one embodiment, the invention includes the use of compound I as purecompounds or admixed with paints including polyurethanes, polysiloxanes,polyacrylates, and other related polymer-based paints and coatings withabout 0.5% polymer based pigment with retention of the thermo chromicbehavior. The thermo chromic polymer-based pigments can be incorporatedvia injection molding or extrusion into many commercially importantplastics such as poly(ethylene terephthalate) (PET), polysytrene,polyethylene (HDPE and LDPE), other polyolefins, polydienes,polycarbonates, polyacrylics, polyacrylic acids, polyacrylamides,polymethacrylics, polyvinyl ethers, polyvinyl halides, poly(vinylnitrile)s poly vinyl esters, polyesters, polysulfones, polysulfonamides,polyamides, polyimines, polyimides, carbohydrates, and polymer mixturesand copolymers. The plastics retain a visually retrievable thermochromic response with pigment loadings of about 0.5% polymer-basedpigment.

In yet another embodiment of the invention, polythiophenes exhibitingcontrolled thermo chromic transitions are dispersed in commerciallyavailable printable ink formulations, e.g. oil with resins, pigmentextenders and other additives, to form thermal indicator ink systems.The polythiophenes are present in the thermal indicator ink in an amountof 1.0-25% by weight based on the total weight of the thermal indicatorink, preferably 7.0 to 14% weight. The ink can be printed usingconventional methods such as ink-jet and letter press. Examples of inkformulations that polythiophene can be dispersed in can includecombinations of resins such as cellulose, nitrocellulose with co-bindersincluding polyamides, polyester amides, alkyd, epoxy acrylates, amineacrylates, polyurethanes, and polyvinyl butyral (UNI-REZ, UNI-JET,BECKOSOL, EPOTUF), suitable oils such as napthenic petroleum oils andvegetable oils, e.g. soy bean oil, and suitable pigment extenders andadditives that can include organic acids and esters of organic acidssuch as malic acid and organic solvents such as 1,5-pentanediol,diethylene glycol, along with other alcohols and related compounds(VERTEC, SYLFAT, UNIKYD, and ICM, DY-SOLVE lines of additives.).

In yet another embodiment the invention, the thermal indicator ink isprinted on at least a portion of a suitable substrate, e.g. a portion ofpaper, plastic, or ceramic food/beverage containers, a portion ofpackaging materials for foods and goods, labels, a portion of labels,stickers, etc., using conventional printing methods. The polythiophenesdispersed in the ink system can be in particulate form and havediameters in the range of between about 0.01-0.1 microns therebyrendering the system suitable for fine printing.

In another embodiment of the invention, the thermal indicator materialis applied to an article, e.g., a portion of paper, plastic or ceramicfood/beverage containers, as a coating on an area of the article, or theentire article, which will be visible during the expected use of thearticle. The coating can be applied by any technique known in the art,such as by brush, roller, spraying, etc. Accordingly, the coatingstypically have a thickness of 0.1 to 1000 microns. The thermal indicatormaterial can also be absorbed on a surface or both absorbed and adsorbedon a surface.

Suitable carrier mediums to be admixed with the polythiophenesexhibiting controlled reversible thermo chromic transitions can includepolyurethanes; elastomers including polysiloxanes and polydienes;polyacrylates, poly(ethylene terephthalate)s (PET), polysytrenes,polyolefins including polyethylenes (HDPE and LDPE) and polypropylene,polycarbonates, polyacrylics, polyacrylic acids, polyacrylamides,polymethacrylics, polyvinyl ethers, polyvinyl halides, poly(vinylnitrile)s polyvinyl esters, polyesters, polysofones, polysulfonamides,polyamides, polyimines, polyimides, and carbohydrates.

The invention will further be described with reference to followingnon-limiting examples.

Example I

The thermal indicator material comprising the polythiophenes exhibitingcontrolled thermo chromic transitions can be prepared via a two stepprocess. Thin films or powders of polythiophenes can be heated above thethermochromic transition, typically 120-150° C., with a heat gun, oven,or hot plate. The samples are typically heated over a short period oftime (5-20 seconds), but slower heating rates are appropriate also,e.g., greater than at least 20 seconds, preferably 20 to 1000 seconds.The heated films or powders are then rapidly removed from the heat,e.g., within a time period of about 0 to 10 seconds, preferably lessthan 2 seconds and cooled via contact with a thermally conductivematerial such as a metal plate. The metal plate can be at roomtemperature or below room temperature as long as it is at least 20° C.below the thermo chromic transition temperature. The contact with thelow temperature thermally conductive surface rapidly cools thepolythiophenes from at or above the thermo chromic transition to within5 to 20° below the thermochromic transition within a time period lessthan 2 seconds, preferably 0.1 seconds, resulting in the production ofthe second low temperature colored material.

The polythiophene films in FIG. 1 have a thermo chromic transition of85° C. The films in FIG. 1 were spin coated from THF solutions of thepolythiophene onto paper. After spin coating, the films were heated witha heat gun to between 120 and 150° C. and then were allowed to slowlycool (>2 seconds) to room temperature to remove any residual solvent.This provided the burgundy film shown in FIG. 1 a. Heating the film asecond time to between 120 and 150° C. for 5 seconds causes the film tochange in color from burgundy to yellow as shown in FIG. 1 b. Afterheating films to between 120 and 150° C. the films can be rapidly cooledby pressing a metal key onto the surface of the film. Cooling to lowtemperature, 0 to 30° C. in 0.1 seconds, allows the generation of anorange mark in the form of a key. The remainder of the film, whichcooled slowly, returns to the original low temperature color, burgundy(FIG. 1 c). If the film is maintained at temperatures below the thermochromic transition of the polythiophene film (85° C.) the mark will beretained for more than a year. However, if the film is heated above 85°C. the mark will disappear. After heating films to between 120 and 150°C. the films can be rapidly cooled by pressing metal fuse onto the film.Rapid cooling to low temperature, 0 to 30° C., allows the generation ofan orange mark in the form of a circle.

The polythiophene films in FIG. 3 have a thermo chromic transition of75° C. The films in FIG. 3 were spin coated from THF solutions of thepolythiophene onto paper. After spin coating, the films were heated witha heat gun to between 120 and 150° C. and then were allowed to slowlycool (>2 seconds) to room temperature to remove any residual solvent.The low temperature films are red. After heating films to between 120and 150° C. for 5 seconds the films can be rapidly cooled by pressing ametal fuse onto the surface of the film. Cooling to low temperature, 0to 30° C., in 0.1 seconds allows the generation of an orange mark in theform of a circle. The remainder of the film, which cooled slowly,returns to the original low temperature color, red (See FIG. 3). If thefilm is maintained at temperatures below the thermo chromic transitionof the polythiophene film (75° C.) the mark will be retained for morethan a year.

The polythiophene films in FIG. 4 have a thermo chromic transition of95° C. The films in FIG. 4 were spin coated from THF solutions of thepolythiophene onto paper. After spin coating, the films were heated witha heat gun to between 120 and 150° C. and then were allowed to slowlycool to room temperature to remove any residual solvent. The lowtemperature films are purple. After heating films to between 120 and150° C. for 5 seconds the films can be rapidly cooled by pressing ametal fuse onto the surface of the film. Cooling to low temperature, 0to 30° C., in 0.1 seconds allows the generation of a red mark in theform of a circle. The remainder of the film, which cooled slowly,returns to the original low temperature color, purple (See FIG. 4). Ifthe film is maintained at temperatures below the thermo chromictransition of the polythiophene film (95° C.) the mark will be retainedfor more than a year.

The foregoing description has been limited to a specific embodiment ofthe invention. It will be apparent, however, that variations andmodifications can be made to the invention, with the attainment of someor all of the advantages of the invention. Therefore, it is the objectof the appended claims to cover all such variations and modifications ascome within the true spirit and scope of the invention.

1. A method for producing a thermal indicator material comprising:providing a plurality of compounds having the following structure:

wherein: R₁-R₆=a hydrogen, substituted or unsubstituted alkyl radical,substituted or unsubstituted alkoxy radical, substituted orunsubstituted thioalkyl radical, substituted or unsubstitutedtrialkylsilyl radical, substituted or unsubstituted acyl radical,substituted or unsubstituted ester radical, substituted or unsubstitutedamine radical, substituted or unsubstituted amide radical, substitutedor unsubstituted heteroaryl or substituted or unsubstituted arylradical; n is between 1 and 1000; m is between 0 and 1000; l is between1 and 1000; and the compounds having a first low temperature color;heating the compounds to a temperature of or above a pre-determinedtemperature to form heated compounds; and cooling the heated compoundsto a temperature within a range of between about 0° C. and 30° C. in atime period of less than 2.0 seconds to form cooled compounds, thecooled compounds exhibiting a second low temperature color andexhibiting a color change from the second low temperature color to thefirst low temperature color when the compounds are exposed to atemperature that meets or exceeds the pre-determined temperature andthen cooled to a temperature within the range of between about 5 to 20°C. below the pre-determined temperature in a time period of greater than2.0 seconds.
 2. The method of claim 1 wherein the heating step comprisesheating the compound for a time period within the range of between about5.0 seconds to 1000 seconds.
 3. The method of claim 1 which furthercomprises admixing the cooled compounds with a carrier medium.
 4. Themethod of claim 3 wherein the cooled compounds are present in thethermal indicator material in an amount of about 0.05 to about 25.0% byweight based on the total weight of the thermal indicator material. 5.The method of claim 1 wherein the pre-determined temperature is in therange of between about −30 to 150° C.
 6. The method of claim 5 whereinthe pre-determined temperature is 85° C., the first low temperaturecolor is burgundy, and the second low temperature is orange.
 7. Themethod of claim 3 wherein the carrier medium is selected from the groupconsisting of polyurethanes; elastomers including polysiloxanes andpolydienes; polyacrylates, poly(ethylene terephthalate)s (PET),polysytrenes, polyolefins including polyethylenes (HDPE and LDPE) andpolypropylene, polycarbonates, polyacrylics, polyacrylic acids,polyacrylamides, polymethacrylics, polyvinyl ethers, polyvinyl halides,poly(vinyl nitrile)s polyvinyl esters, polyesters, polysulfones,polysulfonamides, polyamides, polyimines, polyimides, and carbohydrates.8. The method of claim 3 wherein the carrier medium is an inkformulation.
 9. The method of claim 3 wherein the ink formulationcomprises oils, resins, pigment extenders and additives.
 10. A thermalindicator material comprising: a plurality of compounds having thefollowing structure:

wherein: R₁-R₆=a hydrogen, substituted or unsubstituted alkyl radical,substituted or unsubstituted alkoxy radical, substituted orunsubstituted thioalkyl radical, substituted or unsubstitutedtrialkylsilyl radical, substituted or unsubstituted acyl radical,substituted or unsubstituted ester radical, substituted or unsubstitutedamine radical, substituted or unsubstituted amide radical, orsubstituted or unsubstituted aryl radical; n is between 1 and 1000; m isbetween 0 and 1000; l is between 1 and 1000; the compounds having afirst low temperature color and a second low temperature color; and thecompounds are structured and arranged to exhibit a color change from thesecond low temperature color to the first low temperature color when thethermal indicator material is exposed to a temperature that meets orexceeds a pre-determined temperature and then cooled to a temperature ofwithin the range of between about 0° C. to 30° C. in a time period ofgreater than 2.0 seconds.
 11. The thermal indicator material of claim 10which further comprises a carrier medium.
 12. The thermal indicatormaterial of claim 11 wherein the compounds are present in the thermalindicator material in an amount of about 0.05 to about 25.0% by weightbased on the total weight of the thermal indicator material.
 13. Thethermal indicator material of claim 10 wherein the pre-determinedtemperature is in the range of between about −30 to 150° C.
 14. Thethermal indicator material of claim 10 wherein the pre-determinedtemperature is 85° C. and the first low temperature color is burgundy,and the second low temperature color is orange.
 15. The thermalindicator material of claim 11 wherein the carrier medium is selectedfrom the group consisting of polyurethanes; elastomers includingpolysiloxanes and polydienes; polyacrylates, poly(ethyleneterephthalate)s (PET), polysytrenes, polyolefins including polyethylenes(HDPE and LDPE) and polypropylene, polycarbonates, polyacrylics,polyacrylic acids, polyacrylamides, polymethacrylics, polyvinyl ethers,polyvinyl halides, poly(vinyl nitrile)s polyvinyl esters, polyesters,polysulfones, polysulfonamides, polyamides, polyimines, polyimides, andcarbohydrates.
 16. The thermal indicator material of claim 11 whereinthe carrier medium is an ink formulation.
 17. The thermal indicatormaterial of claim 11 wherein the ink formulation comprises oils, resins,pigment extenders and additives.